Mechanics Flashcards
(71 cards)
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Q
A
2
Q
In real life why does all the kinetic energy in a vehicle travelling on a road,decorating to zero, not get tranferred to potential energy
A
Work is being done against friction / resistive forces
Energy transferred to thermal
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A
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D
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Q
What is terminal velocity
A
The constant velocity reached by an object when the resistive forces balance the driving force
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Q
Define moment of a point
A
Force x perpendicular distance
Between line of action of force and pivot
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State principle of moments
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Sum of clockwise moments is equal to the sum of anticlockwise moments about any given point
For a system in equilbrium
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A
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A
B
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A
As air passes through, temperature increases so it has more energy and so velocity increases
Hence momentum increases
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Weight of the beam is 12,000N. Calculate Tension in AB (T1) and Tension in AC (T2)
A
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A
25
In another test, a spherical particle Q is fired at a right angle to the surface of an
identical block. Q has the same mass as P and is travelling at the same speed as P when it strikes
the surface of the block.
Q is made from a less dense material than P.
Compare the distance travelled by Q with that travelled by P as they are brought to
rest.
Q has a larger volume and has a larger surface area
When Q and P strike the surface, they experience a resistive force that brings them to rest. If this force is mainly due to contact with the medium (e.g., a block or gel), then:
A larger surface area (Q's) experiences greater resistive force (e.g., drag or resistance from the block material).
So Q is brought to rest over a shorter distance compared to P.
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The correct answer is:
A: remains unchanged, same on both masses
Explanation:
In an elastic collision, both kinetic energy and momentum are conserved. Therefore:
Total kinetic energy remains unchanged:
In an elastic collision, the total kinetic energy before and after the collision is conserved, even though individual objects might change their velocities.
Magnitudes of forces are the same on both masses:
According to Newton's Third Law of Motion, for every action, there is an equal and opposite reaction. This means the forces exerted on the two masses during the collision are equal in magnitude but opposite in direction.
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A girl is bouncing on a trampoline.
Assuming that air resistance is negligible, her acceleration
A is zero when she is at maximum height.
B is constant when she is in the air.
C changes direction as she rises and then falls.
D is maximum just before she lands on the trampoline.
B: constant when she is in the air
Explanation:
When the girl is in the air and air resistance is negligible, the only force acting on her is gravity. This means:
Her acceleration is constant and equal to
9.8 m/s^2
downward (acceleration due to gravity).
It does not change direction — gravity always acts downward whether she is going up or coming down.
Why the other options are incorrect:
A: Acceleration is not zero at maximum height — her velocity is zero there, but acceleration remains constant
C: The direction of velocity changes, not acceleration. Acceleration is always downward.
D: The force from the trampoline is maximum just before landing, but the question is about acceleration in the air, not during contact with the trampoline.
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What factors affect terminal velocity of an object
* mass of an object
the larger the mass the larger the terminal velocity reached. As drag force is equal to the weight, hence larger force, larger velocity. Will accelerate more until drag equals weight
* cross-sectional area
larger area increases air resistance acting on object as it falls, decreasing terminal velocity
* Shape
more pointy will experience less drag and have higher terminal
more irregular shape experiences more drag and lower terminal velocity
* density of fluid
the denser the fluid, the greater the drag force . If an object falls through a denser medium it will have lower terminal velocity as drag force is higher in denser fluids
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D
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Both answers are C
27 is C
Because unless they're all in freefall
28 is C
This is linked to your other flashcard on terminal velocity
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Answer is D
P has greater terminal velocity and hits the ground quicker and travels a further distance
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Suggest changes to forces as someone starts climbing the ladder
- as total weight increases (downward force) normal reaction on ground would have to increase to balance this
- if you take moments from the ground, the weight would act in one direction and the resultant force would act in another. Clockwise equals anticlockwise. As person climbs higher resultant force on wall increases
- as resultant force on wall increases, to balance horizontal forces the frictional force on the ground must also increase
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Discuss whether an escape lane containing gravel or an escape ramp would provide the safer experience for the driver of the vehicle as it comes to rest.
The straight road of uniform gradient because:
The deceleration is uniform
with the gravel the initial deceleration is larger/may vary
Travelling through gravel could make the vehicle unstable/bounce
Gravel because:
On the ramp the lorry would roll backwards after stopping
Or because stopping time is longer
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A vehicle is travelling on an escape lane of gravel. State the changes in energy as the vehicle is slowing down and coming to rest
Kinetic energy of vehicle to kinetic energy of gravel / potential energy of gravel
Kinetic energy of gravel to thermal energy of surroundings
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An alternative to an escape lane containing gravel is an escape lane that consists of a
ramp. An escape ramp is a straight road with a concrete surface that has a constant
upward gradient.
One escape ramp makes an angle of 25° to the horizontal and is 85 m long.
Deduce whether this escape ramp is sufficient to stop the vehicle.
Assume that any frictional forces and air resistance that decelerate the vehicle are
negligible.
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Draw resultant force
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C
59
C
Acceleration downwards due to it being freefall
Velocity always follows a tangential path following the motion of the ball
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